Electrophotographic composition and element

ABSTRACT

4-AMINO BENZO(B)PYRYLIUM AND 4-AMINO BENZO(B)THIAPYRLIUM SALTS ARE SENSITIZERS FOR PHOTOCONDUCTORS. PHOTOCONDUCTIVE COMPOSITIONS SENSITIZED WITH THESE COMPOUNDS HAVE INCREASED ELECTROPHOTOGRAPHIC SPEED AND ARE SENSITIVE IN THE ULTRAVIOLET REGION OF THE SPECTRUM.

United States Patent 3,554,745 ELECTROPHOTOGRAPHIC COMPOSITION ANDELEMENT James A. Van Allan, Rochester, -N.Y., assignor to Eastman KodakCompany, Rochester, N.Y., a corporation of New Jersey No Drawing. FiledMar. 29, 1968, Ser. No. 717,373 Int. Cl. G03g 5/00 US. Cl. 961.6 7Claims ABSTRACT OF THE DISCLOSURE 4amino benzo(b)pyrylium and 4-aminobenzo (b)thiapyrylium salts are sensitizers for photoconductors.Photoconductive compositions sensitized with these compounds haveincreased electrophotographic speed and are sensitive in the ultravioletregion of the spectrum.

This invention relates to the novel use of a class of organic compoundsas sensitizers in electrophotographic elements.

The process of xerography, as disclosed by Carlson in US. Pat. No.2,297,691, employs an electrophotographic element comprising a supportmaterial bearing a coating of a normally insulating material whoseelectrical resistance varies with the amount of incident actinicradiation it receives during an imagewise exposure. The element,commonly termed a photoconductive element, is first given a uniformsurface charge after a suitable period of dark adaptation. The elementis then exposed to a pattern of actinic radiation which has the effectof differentially reducing the potential of the surface charge inaccordance with the relative energy contained in various parts of theradiation pattern. The differential surface charge or electrostaticlatent image remaining on the electrophotographic element is then madevisible by contacting the surface with 21 suitable electroscopic markingmaterial. Such marking material or toner, whether contained in aninsulating liquid or on a dry carrier, can be deposited on the exposedsurface in accordance with either the charge pattern or in the absenceof charge pattern as desired. The deposited marking material may then beeither permanently fixed to the surface of the sensitive element byknown means such as heat, pressure, solvent vapor and the like ortransferred to a second element to which it may similarly be fixed.Likewise, the electrostatic latent image can be transferred to a secondelement and developed there.

Various photoconductive insulating materials have been employed in themanufacture of electrophotographic elements. For example, vapors ofselenium and vapors of selenium alloys deposited on a suitable supportand particles of photoconductive zinc oxide held in a resinous,film-forming binder have found wide application in present-day documentcopying applications.

Since the introduction of electrophotography, a great many organiccompounds have been found to possess some degree of photoconductivity.Many organic compounds have revealed a useful level of photoconductionand have been incorporated into photoconductive compositions. Opticallyclear organic photoconductor-containing elements having desirableelectrophotographic properties can be especially useful inelectrophotography. Such electrophotographic elements may be exposed3,554,745 Patented Jan. 12, 1971 through a transparent base, if desired,thereby providing unusual flexibility in equipment design. Suchcompositions when coated as a film or layer on a suitable support alsoyield an element which is reusable; that is, it can be a used to formsubsequent images after residual toner from prior images has beenremoved by transfer and/or clean- Although some of the organicphotocond-uctor materials referred to above are inherently lightsensitive, their degree of sensitivity is usually low and not always ina desired wavelength portion of the spectrum so that it is commonpractice to add materials to increase the speed and to shift thespectral sensitivity.

Increasing the speed and shifting the sensitivity of such systems hasseveral advantages in that it reduces exposure time, allows projectionprinting through various optical systems etc. By increasing the speedthrough the use of sensitizers, photoconductors which would otherwisehave been unsatisfactory are useful in processes Where higher speeds arerequired. However, a major disadvantage of many prior sensitized organicphotoconductor systems has been the highly colored nature of suchsystems.

It is, therefore, an object of this invention to provide a novel classof sensitizers for use in combination With organic photoconductors.

Another object of this invention is to sensitized photoconductiveelements.

A further object of this invention is to provide novel photoconductivecompositions which are colorless and are sensitive to ultravioletradiation.

These and other objects are accomplished by the use of 4-aminobenzo(b)pyrylium and 4-amino benzo(b) thiapyrylium salts as sensitizersin organic photoconductor-containing systems. Typical sensitizers of thepresent invention include those having the following structural formula:

provide novel wherein X is a sulfur atom or an oxygen atom;

Z is an anionic function including such acid anions as perchlorate,fluoroborate, sulfonate, periodate, p-toluenesulfonate etc.;

R is an alkyl radical of from 1 to 10 carbon atoms, such as methyl,ethyl, isopropyl, n-butyl, pentyl, octyl, decyl etc. includingcycloalkyl such as cyclopentyl, cyclohexyl etc., as Well as suchsubstituted alkyl radicals as aralkyl radicals having from 1 to 4 carbonatoms in the alkyl moiety such as benzyl, phenylethyl, phenylpropyl andphenylbutyl, an aryl radical as phenyl and naphthyl radicals, and thelike;

R is a hydrogen atom, a lower alkyl radical of from 1 to 4 carbon atomssuch as methyl, ethyl, isopropyl, butyl etc. and a lower alkoxy radicalhaving from 1 to 4 carbon atoms in the alkyl moiety such as methoxy,ethoxy, propoxy, butoxy etc.; and

R and R when taken separately each represents a hydrogen atom and Whentaken together are attached to adjacent carbon atoms and represent theatoms necessary to form a fused aromatic ring such as a benzo ring andincluding substituted fused aromatic rings.

Suitable sensitizers would include the following representativecompounds:

TABLE A 4-benzylamino-2-phenylbenzo [b] pyrylium perchlorate4-anilino-2- 4-rnethoxyphenyl naphtho 1,2-b] pyrylium perchlorate 1-[N-butylamino] -3-phenylnaphtho [2, 1-b] pyryliurn perchlorate 4-(N-butylamino -2- (4-methoxyphenyl) naphtho- 1,2-b]pyryl1um perchlorate1-anilino-3-phenylnaphtho[2,1 b]pyrylium perchlorate 4-[N-butylamino]-2-phenylbenzo [b] thiapyrylium perchlorate 4-anilino fiavyliumperchlorate 4-cyclohexylamino-2-phenylbenzo [b] thiapyrylium perchlorate4- ['N-octylamino] -2-phe'nylbenzo [b] thiapyrylium perchlorate4-phenylamino-2-phenylbenzo [b] thiapyrylium perchlorate2-phenyl-4-phenethylaminobenzeno [b] thiapyrylium perchlorate 4-[N-butylamino] -2(p-methoxyphenyl)benzo [b] pyrylium fluoroborate 4-[N-butylamino] -2(p-methoxyphenyl)benzo [b] pyrylium perchlorateElectrophotographic elements of the invention can be prepared with avariety of organic photoconductive compound and the sensitizingcompounds of this invention in the usual manner, i.e., by blending adispersion or solution of the photoconductive compound together With anelectrically insulating, film-forming resin binder when necessary ordesirable and coating or forming a selfsupporting layer with thephotoconductive composition. Generally, a suitable amount of thesensitizing compound is mixed with the photoconductive coatingcomposition so that after thorough mixing the sensitizing compound isuniformly distributed throughout the desired layer of the coatedelement. The amount of sensitizer that can be added to a photoconductorcontaining layer to give effective increases in speed can vary widely.The optimum concentration in any given case will vary with the specificphotoconductor and sensitizing compound used. In general, substantialspeed gains can be obtained where an appropriate sensitizer is added ina concentration range from about 0.0001 to about 30 percent by weightbased on the weight of the film-forming coating composition. Normally, asensitizer is added to the coating composition in an amount from about0.005 to about 5.0 percent by weight of the total coating composition.

The sensitizers of this invention are effective for enhancing theelectrophotosensitivity of a wide variety of photoconductors. Thepreferred photoconductors are those organic compounds which exhibit anelectrophotosensitivity to light and are capable of forming transparentelements. A useful class of organic photoconductors is referred toherein as organic amine photoconductors. Such organic photoconductorshave as a common structural feature at least one amino group. Usefulorganic photoconductors which can be spectrally sensitized in accordancewith this invention include, therefore, arylamine compoundscomprising 1) diarylamines such as diphenylamine, dinaphthylamine, N,N'-diphenylbenzidine, N-phenyl-l-naphthylamine, N-phenyl- Z-naphthylamine,N,N diphenyl p phenylenediamine, 2-carboxy 5chloro-4'-methoxydiphenylamine, 6-anilinophenol, N,N' di 2naphthyl-p-phenylenediamine, the materials described in Fox US. Pat.3,240,597, is sued Mar. 15, 1966, and the like, and (2) triarylaminesincluding (a) nonpolymeric triarylamines, such as triphenylamine,N,N,N',N-tetraphenyl m phenylenediamine; 4 acetyltriphenylamine, 4hexanoyltriphenylamine; 4 lauroyltriphenylamine, 4 hexyltriphenylamine,4-dodecyltriphenylamine, 4,4 bis(diphenylamino)benzyl, 4,4bis(diphenylamino) benzophenone and the like and (b) polymerictriarylamines such as poly[N,4"-(N, N,N' triphenylbenzidine)],polyadipyltriphenylamine, polysebacyltriphenylamine, polydecamethylenetriphenylamine; poly N (4-vinylphenyl)diphenylamine, poly-N-(vinylphenyl) a,a' dinaphthylamine and the like. Other usefulamine-type photoconductors are disclosed in US. Pat. 3,180,730, issuedApr. 27, 1965. In addition, photoconductive substances capable of beingspectrally sensitized in accordance with this invention are disclosed inFox US. Pat. 3,265,496, issued Aug. 9, 1966, and include thoserepresented by the following general formula:

wherein A represents a mononuclear or polynuclear divalent aromaticradical, either fused or linear (e.g., phenyl, naphthyl, biphenyl,binaphthyl, etc.) or a substituted divalent aromatic radical of thesetypes wherein said substituent can comprise a member such as an acylgroup having from 1 to about 6 carbon atoms (e.g., acetyl propionyl,butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms(e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from1 to about 6 carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy,etc.) or 2. nitro group; A represents a mononuclear or polynuclearmonovalent aromatic radical, either fused or linear (e.g., phenyl,naphthyl, biphenyl, etc.) or a substituted monovalent aromatic radicalwherein said substituent can comprise a member such as an acyl grouphaving from 1 to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl,etc.), an alkyl group having from 1 to about 6 carbon atoms (e.g.,methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from 1 toabout 6 carbon atoms (e.g., methoxy, propoxy, pentoxy, etc.) or a nitrogroup; Q can represent a hydrogen atom, a halogen atom or an aromaticamino group, such as A'NH; b represents an integer from 1 to about 12;and G represents a hydrogen atom, a mononuclear or polynuclear aromaticradical, either fused or linear (e.g., phenyl, naphthyl, biphenyl,etc.), a substituted aromatic radical wherein said substituent comprisesan alkyl group, an alkoxy group, an acyl group, a nitro group or a poly-(4-vinylphenyl) group which is bonded to the nitrogen atom by a carbonatom of the phenyl group.

Polyarylalkane photoconductors are particularly useful in accordancewith the present invention. Such photoconductors are described in US.Pat. 3,274,000; French Pat. 1,383,461 and in copending application ofSeus and Goldman entitled Photoconductive Elements Containing OrganicPhotoconductors filed Apr. 3, 1967. These photoconductors include leucobases of diaryl or triarylmethane dye salts, 1,1,1-triarylalkaneswherein the alkane moiety has at least two carbon atoms andtetraarylmethanes, there being substituted an amine group on at leastone of the aryl groups attached to the alkane and methane moieties ofthe latter two classes of photoconductors which are non-leuco basematerials.

Preferred polyaryl alkane photoconductors can be represented by theformula:

wherein each of D, E and G is an aryl group and J is a hydrogen atom, analkyl group, or an aryl group,

wherein each L can be an alkyl group typically having 1 to 8 carbonatoms, a hydrogen atom, an aryl group or together the necessary atoms toform a heterocyclic amino group typically having to 6 atoms in the ringsuch as morpholino, pyridyl, pyrryl, etc. At least one of D, E and G ispreferably p-dialkylaminophenyl group. When I is an alkyl group, such analkyl group more generally has 1 to 7 carbon atoms.

Representative useful polyarylalkane photoconductors include thecompounds listed below:

TABLE B Wherein R and R are each phenyl radicals including substitutedphenyl radicals and particularly when R is a phenyl radical having theformula:

where R and R are each aryl radicals, aliphatic residues of 1 to 12carbon atoms such as alkyl radicals preferably having 1 to 4 carbonatoms or hydrogen. Particularly advantageous results are obtained when Ris a phenyl radical including substituted phenyl radicals and where R isdiphenylaminophenyl, dimethylaminophenyl or phenyl.

Preferred binders for use in preparing the present photoconductivelayers comprise polymers having fairly high dielectric strength whichare good electrically insulating film-forming vehicles. Materials ofthis type comprise styrene-butadiene copolymers; silicone resins;styrene-alkyd resins; silicone-alkyd resins; soya-alkyd resins; poly(vinyl chloride); poly(vinylidene chloride); vinylidenechloride-acrylonitrile copolymers; poly(viny1 acetate); vinylacetate-vinyl chloride copolymers; poly(vinyl acetals), such aspoly(vinyl butyral); polyacrylic and methacrylic esters, such aspoly(methylmethacrylate), poly (n-butylmethacrylate), poly(isobutylmethacrylate), etc.;

Compound name Compound No.:

4,4'benzylidine-bis(N,N-dietl1yl-m-toluidine) 4',4"-diamino-4-dimethy1amino-2',2"-dimethyltriphenylmethane.

4 ,4"-bis (diethylamino) -4-dimethylamino-2,2"-dimethyltriphenylmethane.

(7) 4 ,4-bis(diethylamino)-2-chloro-2,2"-dimethyl-4-dimethylaminotriphenylrnethane.(8) 4,4"-bis(diethylamino)-4-dimethylarnino2,2,2"-trimethyltriphenylmethane. (9) 4 ,4"-bis(dimethylamino),2-chloro-2 ,2"-din1ethyltriphenylmethane. (10) 4',4"-bis(dimethylamino) -2' ,2-dimethyl4-methoxytriphenylmethane. (11)Bis(4-diethylamino)-1,1,1-triphenylethane. (12).Bis(4-diethylamino)tetraphenylmethane. (13)-4,4"-bis(benzylethylamino)-2,2"-dimethyltriphenylmethane. (14).4,4"-bis(diethylamino)2',2-diethoxytriphenylmethane.

(15)- 4,4-bis(d.imethylamino)-1,1,1-triphenylethane. (16)-1-(4-N,N-dimethylaminophenyl)-1,l-dipheny1ethane. gflguu4-dinfiethylaminotetraphenylmethane.

Additional organic photoconductors which can be employed with thesensitizing compounds described herein are non-ionic cycloheptenylcompounds such as those described in copending application Ser. No.654,091, filed July 1-8, 1967; the N,N-bicarbazyls and tetra-substitutedhydrazines; the 3,3 bis 1,5-diarylpyrazolines; triarylamines having atleast one of the aryl radicals substituted by either a vinyl radical, ora vinylene radical having at least one active hydrogen-containing groupsuch as pdiphenylaminocinnamic acid; triarylamines substituted by anactive hydrogen-containing group, e.g., 4-carboxytriphgtylamine; andthose described in Australian Pat.'No. 248,402.

Another class of photoconductors useful in this invention are the4-diarylamino-substit-uted chalcones. Typical compounds of this type arelow molecular weight nonpolymeric ketones having the general formula:

polystyrene; nitrated polystyrene; polymethylstyrene; isobutylenepolymers; polyesters, such as poly(ethylene alkaryloxyalkyleneterephthalate); phenol-formaldehyde resins; ketoneresins; polyamides;polycarbonates; polythiocarbonates; poly (ethyleneglycol cobishydroxyethoxyphenyl propane terephthalate); nuclear substitutedpolyvinyl haloarylates; etc. Methods of making resins of this type havebeen described in the prior art, for example, styrene-alkyd resins canbe prepared according to the method described in US Pats. 2,361,019 and2,258,423. Suitable resins of the type contemplated for use in thephotoconductive layers of the invention are sold under such trade namesas Vitel PE-101, Cymac, Piccopale 100, Saran F-220 and Lexan 105. Othertypes of binders which can be used in the photoconductive layers of theinvention include such materials as parafi'in, mineral waxes etc.

Solvents of choice for preparing coating compositions of the presentinvention can include a number of solvents such as benzene, toluene,acetone, Z-butanone, chlorinated hydrocarbons, e.g., methylene chloride,ethylene chloride, etc., ethers, e.g., tetrahydrofuran, or mixtures ofthese solvents, etc.

In preparing the coating composition useful results are obtained wherethe photoconductor substance is present in an amount equal to at leastabout 1 weight percent of the coating composition. The upper limit inthe amount of photoconductor substance present can be widely varied inaccordance with usual practice. In those cases where a binder isemployed, it is normally required that the photoconductor substance bepresent in an amount from about 1 weight percent of the coatingcomposition to about 99 weight percent of the coating composition. Apreferred weight range for the photoconductor substance in the coatingcomposition is from about 10 Weight percent to about 60 weight percent.

Coating thicknesses of the photoconductive composition on a support canvary widely. Normally, a coating in the range of about 0.001 inch toabout 0.01 inch before drying is useful for the practice of thisinvention. The preferred range of coating thickness is found to be inthe range from about 0.002 inch to about 0.006 inch before dryingalthough useful results can be obtained outside of this range.

Suitable supporting materials for coating the photoconductive layers ofthe present invention can include any of a wide variety of electricallyconducting supports, for example, paper (at a relative humidity abovepercent); aluminum-paper laminates; metal foils such as aluminum foil,zinc foil, etc.; metal plates, such as aluminum, copper, zinc, brass andgalvanized plates; vapor deposited metal layers such as silver, nickel,aluminum and the like coated on paper or conventional photographic filmbases such as cellulose acetate, polystyrene, etc. Such conductingmaterials as nickel can be coated by vacuum deposition on transparentfilm supports in sufiiciently thin layers to allow electrophotographicelements prepared therewith to be exposed from either side of suchelements. An especially useful conducting support can be prepared bycoating a support material such as poly(e'thylene terephthalate) with aconducting layer containing a semiconductor dispersed in a resin. Suchconducting layers both with and without insulating barrier layers aredescribed in US. Pat. 3,245,833. Likewise, a suitable conducting coatingcan be prepared from the sodium salt of a carboxyester lactone of maleicanhydride and a vinyl acetate polymer. Such kinds of conducting layersand methods for their optimum preparation and use are disclosed in US.3,007,901 and 3,267,807.

The elements of the present invention can be employed in any of thewell-known electrophotographic processes which require photoconductivelayers. One such process is the aforementioned xerographic process. Asexplained previously, in a process of this type the electrophotographicelement is given a blanket electrostatic charge by placing the sameunder a corona discharge which serves to give a uniform charge to thesurface of the photoconductive layer. This charge is retained on thelayer by virtue of the substantial insulating property of the layer,i.e., the low conductivity of the layer in the dark. The electrostaticcharge formed on the surface of the photoconducting layer is thenselectively dissipated from the surface of the layer by exposure tolight through an image-bearing transparency by a conventional exposureoperation such as, for example, by contact-printing technique, or bylens projection of an image, etc., to form an electrostatic latent imagein the photoconducting layer. By exposure of the surface in this manner,a charged pattern is created by virtue of the fact that light causes thecharge to be conducted away in proportion to the intensity of theillumination in a particular area. The charge pattern remaining afterexposure is then developed, i.e., rendered visible, by treatment with amedium comprising electrostatically attractable particles having opticaldensity. The developing electrostatically attractable particles can bein the form of a dust or a pigment in a resinous carrier or a liquiddeveloper can be used in which the devel- 8 oping particles are carriedin an electrically insulating liquid carrier. Methods of development ofthis type are widely known and have been described in the patentliterature in such patents, for example, as US. 2,297,691 and inAustralian Pat. 212,315. In processes of electrophotographicreproduction such as in xerography, by selecting a developing particlewhich has a low-melting resin as one of its components, it is possibleto treat the developed photoconductive material with heat and cause thepowder to adhere permanently to the surface of the photoconductivelayer. In other cases, a transfer of the image formed on thephotoconductive layer can be made to a second support which would thenbecome the final print. Techniques of the type indicated are well knownin the art and have been described in a number of US. and foreignpatents such as U.S. Pats. 2,297,691 and 2,551,582 and in RCA Review,vol. 15 (1954), pages 469-484.

An increasing use of electrophotographic elements has occurred in thefield of recording data displayed on a cathode-ray tube. Advantagesgained through such use include attractively high photographic speed,desirable spectral response, and short time of access to a visiblerecorded image.

It is frequently desirable to employ the image-bearingelectrophotographic element having a transparent film base as a masterfrom which further prints can be generated. Such elements can be used asmasters in many types of reproduction processes. Typical of theseprocesses are the rerographic process, thermographic process, directelectrostatic process, stabilization process, gelatin transfer process,diifusion transfer process, etc. A particularly advantageous process bywhich such a print can be made is the diazo process. In this process, adiazonium saltcontaining element is exposed through a transparentelectrophotographic original bearing a developed or toned image toactivating radiation from an ultraviolet source. The exposure causesdecomposition of the salt in those areas which are struck by activatingradiation. Subsequently, the exposed diazo element is passed through anatmosphere of a suitable alkaline material, such as ammonia vapor. Inthe presence of the alkaline material and a dye-forming coupler, whichcan be either incorporated in the diazonium-containing layer orintroduced during the development step, the diazonium salt which is not0 decomposed by exposure is converted to an azo dye. A

positive reproduction of the original is formed.

A difliculty commonly encountered in the production of copies fromsensitized photoconductor-containing coated elements is that thephotoconductive element possesses a relatively high optical opacityresulting from coloration imparted by the sensitizedphotoconductor-containing composition. As a result the element does nottransmit sufficient radiation in that portion of the electromagneticspectrum to which the copy element is sensitive. Therefore, reprints arevery difiicult to obtain. Also, if the image-bearing elements are to beused for direct reading, the image portions of the elements are oftenalmost indiscernible due to the lack of contrast. One solution proposedfor this problem has been to bleach the highly colored photoconductiveelements. However, with the present class of sensitizers a colorlessphotoconductive layer results which eliminates the need for an extrableaching step.

The following examples are included for a further runderstanding of theinvention.

EXAMPLE 1 A control coating is prepared from the following ingredients:

wPoly[ethyleneglycol-co-bis (hydroxyethoxyphenyl) propane terephthalate](binder)1.5 g.

(Triphenylamine (photoconductor)0.5 g.

Methylene chloride (s0lvent)l 1.7 ml.

The above homogeneous photoconductive composition is coated at a wetthickness of 0.004 inch onto a poly(ethylene terephthalate) film supportcarrying a conductive layer of the sodium salt of a polymeric lactone asdescribed in U.S. Pat. No. 3,260,706. The coating block temperature ismaintained at 90 F. The resulting element is called Element I (control).The above procedure is repeated with the addition of 0.2 g. of4N-butylamino-2- (4-methoxyphenyl)benzo(b)pyrylium perchlorate as thesensitizer prior to coating. The resultant element is called Element H.Next, an element similar to Element I is prepared using 0.5 g. of4,4'-benzylidene-bis(N,N-diethyl-mtoluidine) in place of the previousphotoconductor. The resultant element is called Element III (control).Finally, Element IV is prepared using the photoconductive composition ofElement III plus 0.02 g. of 4-N-butylamino-2- (4-methoxyphenyl)benzo(b)pyrilium perchlorate as the sensitizer. The resultantelectrophotographic elements are then electrostatically charged under acorona source until the surface potential, as measured by ,anelectrometer probe, reaches about 600 volts. The charged elements arethen exposed to a 3000 K. tungsten light source through a steppeddensity gray scale. The exposure causes reduction of the surfacepotential of the elements under each step of the gray scale from itsinitial potential, V to some lower potential, V, whose exact valuedepends on the actual amount of exposure in meter-candle-secondsreceived by the area. The results of these measurements are then plottedon a graph of surface potential V vs. log exposure for each step. Theactual positive or negative speed of the photoconductive compositionused can then be expressed in terms of the reciprocal of the exposurerequired to reduce the surface potential to any fixed arbitrarilyselected value. Herein, unless otherwise stated, the actual positive ornegative speed is the numerical expression of 10 divided by the exposurein meter-candleseconds required to reduce the 600 volt charged surfacepotential to a value of 500 volts (100 volt shoulder speed) or to avalue of 100 volts (100 volt toe speed). The speeds of the elements arerecorded in Table I below.

TABLE I.ELECTROPHOTO GRAPHIC SPEEDS These elements can be charged,exposed and developed with liquid developers of the type described inUS. Pat. No. 2,907,674 to form visible images.

EXAMPLE 2 Another element (5) similar to Element II of Example 1 isprepared. The element is then charged to a positive polarity of 610 v.and exposed to a zenon light source through a 1.9 neutral density filterin combination with a set of filters simulating the wavelengthdistribution of P-16 phosphor emission. P-16 phosphors are standardmaterials used in cathode ray tubes, have a fluorescent color ofultraviolet to blue, have a typical wavelength peak at 3800 A. andcomprise calcium magnesium silicate doped with cesium. Upon exposure theelement photodecays to a 50 v. surface potential in only 13.5 seconds.An element (6) similar to Element IV is prepared by usingpolyvinyl-m-bromobenzoate-co-vinylacetate as the binder. This elementgives a similar response to the P16 phosphor simulation photodecay test.These elements can then bechargcd, exposed and developed with a liquiddeveloper of the type described in US. Pat. No. 2,907,674 to formvisible images.

EXAMPLE 3 Four electrophotographic elements are prepared as above using1.5 g. of binder, 0.5 g. of photoconductor, 11.7 ml. of solvent and 0.01to 0.02 g. of sensitizer where used. The binders used are (a)poly(vinyl-m-bromobenzoate-co-vinyl-acetate) and (b) a polycarbonateresin formed from the reaction between phosgene and adihydroxydiarylalkane or from the ester exchange reaction betweendiphenylcarbonate and 2,2-bis-4-hydroxyphenylpropane (Lexan 145 resin,General Electric Company). The photoconductor used is4,4'-benzylidene-bis(N,N-diethyl-m-toluidine). The sensitizer used is4-N-butylamino- 2-(4-methoxy-phenyl) benzo (b)pyrylium perchlorate. Theelements are then subjected to an ultraviolet (365 m photodecay test asin Example 2 by charging to a positive and/or a negative 600 v. surfacecharge and exposing until the potential decays to v. The results ofthese tests are shown in Table 11 below.

TABLE II 100 v. photodecay time, see. Amounts of Binder sensitizer, g.

Element No.:

Element 7 has only a 27.5% absorption at 365 m whereas Element 8 has an84.5% absorption at 365 mg. After testing Elements 8 and 10 can becharged, exposed and developed as above.

EXAMPLE 4 Five elements are prepared in accordance with Example 1 using1.5 g. of the binder of Element I, 0.5 g. of one of the followingphotoconductors (1) triphenylamine, (2)1-(p-diphenyl-aminophenyl)ethanol, (3) 4-hydroxymethyl triphenylamine,and (4) B-(N,N-diphenylamino)propionic acid and 0.06 or 0.02 g. of thesensitizer 4-N-butylamino-2-(4-methoxyphenyl) benzo(b)-pyryliumperchlorate. The elements are then measured for the 100 volt shoulderspeeds as in Example 1. The results of these measurements are shown inTable III below.

A variety of electrophotographic elements are prepared in accordancewith Example 1. The photoconductive compositions contain the binder ofElement I with 20% by weight of one of the following photoconductors (A)triphenylamine, (B) 4,4-benzylidene-bis(N,N-diethyl-m-toluidine) or (C)4,4'-bis(diphenylaminochalcone) and 0.8% by weight of a sensitizer aslisted below. The resultant elements are then measured for positive andnegative 100 v. shoulder speed as before. The results of thesemeasurements are shown in Table IV below:

ing binder material and having dispersed therein a sensitizing amount ofa member selected from the group con- TABLE IV 100 v. shoulderPhotospeed conductor Sensitizer Element No 17-benzylamino-2-phenylbenzo[b]pyrylium perchlorate A 140 112 do B 110 8 C450 280 A 250 100 B 63 d0 t a C 320 160l-[N-butylamin0]-3-phenylnaptho[2,1-b]pyrylium perchlorate A 220 .do t B105 C 300 250 A. 250 100 B 160 130 C 180 100 A 100 0 B 50 11 31 C 400100 32 A 100 B 120 63 C 360 100 A 63 50 B 32 36 d0 C 500 2004-cyclohexylamino-2-phenylbcnzo[b]thia-pyrylium perchlorate. A 120 l o B120 140 l.d0 C 560 200 4[N-octy1amino]-2-phenylbenzo-[b]thiapyryliumperchlorate. A 180 110 o B 180 80 C 320 200 A 100 50 B 16 9. 0 C 400 80A 280 90 B 220 200 C 450 250 A 160 B 160 63 C 250 110 A 250 200 B 140200 C 160 63 The absorption maximum is measured for each of Elements17-21 and is found to be in the ultraviolet region in all instances.

EXAMPLE 6 Several electrophotographic elements are prepared inaccordance with Example 1 using poly(vinyl-m-bromobenzoate-co-vinylacetate) as the binder with 25% by weight of4,4'-benzylidene-bis(N,N-diethyl-m-toluidine) as the photoconductor andl to 3% by weight of the sensitizer 4-N-butylan1ino-2-(4-methoxyphenyl)benzo(b) pyrylium perchlorate. The various elements are then subjectedto a Pl6 phosphor simulation photodecay test as in Example 2. Theelements are charged to a positive polarity of about 600 v. and exposed.The elements are allowed to photodecay to 100 and to 50 v.,respectively, and the time is measured. The results are shown below.

TABLE V Photodecay time, sec. Amount of sensitizcr (percent by weight)100 v. 50 v.

sisting of 4-aminobenzo(b)pyrylium and 4-aminobenzo (b)thiapyryliumsalts having the formula:

X is selected from the group consisting of a sulfur atom and an oxygenatom;

Z is an anion;

R is selected from the group consisting of an alkyl radical and an arylradical;

R is selected from the group consisting of a hydrogen atom, a loweralkyl radical and a lower alkoxy radical; and

R and R when taken separately, each represents a hydrogen atom, and whentaken together, are attached 0 adjacent carbon atoms and represent theatoms necessary to form a fused aromatic ring.

2. A photoconductive composition as in claim 1 wherein the sensitizingsalt is selected from the group consisting of:

wherein 4-benzylamino-2-pheny1ben2o [b] pyrylium perchlorate,

4-anilino-2- (4-methoxyphenyl naphtho[ 1,2-b pyrylium perchlorate,

1-[N-butylamino1-3 -phenylnaphtho [2,1-b]pyrylium perchlorate,

4-(N-butylarnino)-2-(4-methoxyphenyl)naphtho[1,2-b]

pyrylium perchlorate,

l-anilino-3-phenylnaphtho [2,1-b]pyrylium perchlorate,

4-[N-octylamino]-2-phenylbenzo [bjthiapyrylium perchlorate,

triphenylamine,

4,4'-benzylidene-bis (N,N-diethyl-m-toluidine) 1- (p-diphenylaminophenyl) ethanol, 4-hydroxymethyl triphenylamine,

;8- (N,N'-diphenylamino propionic acid, and4,4'-bis(diphenylaminochalcone) 4. An electrophotographic elementcomprising a support having coated thereon a layer of an electricallyinsulating binder material having dispersed therein an organicphotoconductor and a sensitizing amount of a member selected from thegroup consisting of 4-aminobenzo(b)pyrylium and 4aminobenzo(b)thiapyrylium salts having the formula:

wherein:

X is selected from the group consisting of a sulfur atom and an oxygenatom;

Z is an anion;

R is selected from the group consisting of an alkyl radical and an arylradical;

R is selected from the group consisting of a hydrogen atom, a loweralkyl radical and a lower alkoxy radical; and

R and R when taken separately, each represents a hydrogen atom, and whentaken together, are attached to adjacent carbon atoms and represent theatoms necessary to form a fused aromatic ring.

5. An electrophotographic element as in claim 4 wherein the senstizingsalt is selected from the group consisting of:

4-benzylamino-2-phenylbenzo [b]pyrylium perchlorate,

4-ani1ino-2- (4-methoxyphenyl naphtho 1,2-b1pyrylium perchlorate,

1-[N-butylamino]-3-phenylnaphtho[2,1-b1pyrylium perchlorate,

4- N-butylamino) -2- (4-methoxyphenyl naphtho-[ 1,2-b]

pyrylium perchlorate,

1-anilino-3-phenylnaphtho[2,1-b]pyrylium perchlorate,

4-[N-butylamin0] -2-phenylbenzo [b] thiapyrylium perchlorate,

4-anilino flavylium perchlorate,

4-cyclohexylamino-2-phenylbenzo [b] thiapyrylium perchlorate,

4- [N-octylamino] -2-phenylbenzo [b] thiapyrylium perchlorate,

4-phenylamino-Z-phenylbenzo [b]thiapyry1ium perchlorate,

2-phenyl-4-phenethylaminobenzo [b] thiapyrylium perchlorate,

4- [N-butylamino] -2-(p-methoxyphenyl)benzo [b] pyrylium fluoroborate,and

4- [N-butylamino] -2- (p-methoxyphenyl) benzo [b pyrylium perchlorate.

6. An electrophotographic element as in claim 4 wherein the organicphotoconductor is selected from the gr up consisting of: triphenylamine,4,4'-benzylidene-bis (N,N-diethylm-toluidine) 1- (p-diphenylaminophenyl)ethanol, 4-hydroxymethyl triphenylamine,

r ,8-(N,N'-diphenylamino)propionic acid, and

4,4-bis (diphenylaminochalcone) 7. An electrophotographic element as inclaim 4 wherein the support is electrically conducting.

References Cited UNITED STATES PATENTS 3,250,615 5/1966 Van Allan et a1.961 3,397,086 8/1968 Bartfai 961.5X

GEORGE F. LESMES, Primary Examiner M. B. WITI'ENBERG, Assistant ExaminerU.S. Cl. X.R.

@2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,55 +,7 +5 Dated January 12. 1971 Inventor) James A. VanAllan It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 13, line 1]., "h-Ebutylaming? should read "h-[fi-butylamingT';and

Column 14, line 2, "senstizing" should read "sensitizing".

Signed and sealed this 21 th day of August 1971.

(SEAL) Attest:

EDWARD M.FLET0HER,JR.

WILLIAM E. son LE Attesting Officer W Commissioner of Patents

